Turbomachines such as gas turbine engines include a fan section, a compressor section, a combustion section, and a turbine section. A shaft extends axially through the engine from the fan section through the turbine section and rotates axially spaced apart stages of disks; the shaft is typically supported by two axially spaced apart bearing assemblies that are connected to the case by a bearing support housing. In many engine designs, a combination of ball and roller bearings are used, although the use of two ball bearing assemblies is known. A key requirement of any bearing assembly is that it supports the shaft in such a manner that vibration of the bearings as well as the shaft during engine operation is minimized, even at very high shaft rotation speeds.
Typically, during the operation of an aircraft gas turbine engine, a load is applied to one or both of the radially spaced apart bearing races that surround the bearings therebetween. Application of a load onto the races brings them into line-on-line running contact with their respective balls, thereby reducing the vibration that would otherwise take place within the bearing assembly. It is known to use air pressure to load the bearings; however, the application of air pressure can be unreliable, because during engine operation, the magnitude of the applied pressure may be too low to effectively load the bearings, which can result in excessive vibration of the bearings and the shaft, which can generate an undesirable level of noise within the aircraft cabin.
In addition to the air pressurizing method for loading bearing structures, other designs are shown in U.S. Pat. Nos. 3,574,424, 4,159,808, 4,268,220, 4,578,018, and 5,105,295. Notwithstanding the existence of these designs, improved designs are required to provide optimum operating characteristics for advanced engines. The present invention satisfies this industry need.